1. Field of Invention
The present invention relates to an emission device, a surface light source device and a display, being applied to various devices such as emission devices or surface light source devices for backlight arrangement of liquid crystal display panel or general uses of illumination, for example, interior illumination. The present invention is also applied to surface light source devices employing emission devices and displays employing combination of emission device and object-to-be-illuminated for displaying.
2. Related Arts
It has been broadly known to employ a surface light source device provided with a plurality of point-like-light-sources as an illumination means for liquid crystal display monitor of devices such as personal computer or television set. A popular point-like-light-source is LED (Light Emitting Diode). According to typical arts, such a surface light source device used for illuminating a LCD-panel of LCD-monitor is provided with a plurality of LEDs and a plate-like light flux control member size and shape of which are generally the same as those of the LCD-panel.
The LEDs are disposed like a matrix on the back face side of the light flux control member. Light from LEDs enters into the light flux control member from the back face side thereof, being emitted an emission face opposite to the back face of the light flux control member after travelling within the light flux control member. The emitted light is supplied to LCD-panel for backlighting. Prior arts disclosed in known documents are as follows.
<First Prior Art>
FIG. 28 is a diagram illustrating an example of skeleton structure of surface light source device employing a plurality of LEDs as primary light source. Such skeleton structure is disclosed in Document 1 noted below. Referring to FIG. 28, surface light source device 100 is provided with a plurality of LEDs 101 and micro-lens-array 102. Micro-lens-array 102 consists of micro-lenses arranged in one-to-one correspondence with respect to LEDs 101. Light from EDs 101 is emitted upward in the illustration through micro-lens-array 102.
<Second Prior Art>
FIG. 29 is a diagram illustrating an example of skeleton structure of emission display employing a LED as primary light source. Such skeleton structure is disclosed in Document 2 noted below. Referring to FIG. 29, emission display 103 is provided with LED 104, concave lens 105 and convex lens 106. Light from ED 104 is converged by convex lens 106 after being diverged by concave lens 105, being emitted to directions generally parallel to an optical axis of LED 104.
<Third Prior Art>
An known display employing a LED is disclosed in Document 3 noted below. FIG. 30 shows an arrangement in display 107 for illumination. The arrangement comprises LED 108, converging lens 110 and diverging lens 111. Light from LED 108 is converged by converging lens 110 to be directed forward, then being diverged by diverging lens 111.
<Fourth Prior Art>
FIG. 31 shows an example of arrangement including an object-to-be-illuminated in a display employing LEDs as primary light source. Referring to FIG. 31, display 121 is provided with a plurality of LED chips 125, light diffusion member 126 and object-to-be-illuminated (such as LCD-panel) 127. Each LED chip 125 is provided with LED 124. Light flux control member 123 provided with a hemisphere emission face 122 is fixed to a light emitting surface side of LED 124. Light from each LED chip is supplied to object-to-be-illuminated (such as LCD-panel) 127 after transmitting light diffusion member 126. Thus object-to-be-illuminated 127 is illuminated two-dimensionally.
<Fifth Prior Art>
FIG. 32 illustrates another example of display employing a LED as primary light source. Such skeleton structure is disclosed in Document 4 noted below. Referring to FIG. 32, matrix-type display 130 is provided with display panel substrate 131, emission elements 132 arrayed thereon like matrix and lens case 133. Lens case 133 is located at a front side of emission elements 132, being mounted as to be in closely contact with display panel substrate 131.
Hemisphere-like projection portions 134 are formed on lens case 133 as to correspond respectively to emission elements 132. Hollow 135 is formed within each projection portion 134 for accommodating emission element 132. Each hollow 135 has a side wall which is formed so refract and take in light from emission element 132 so that light thus taken in is directed to a front side (upward direction in FIG. 32).
In other words, light from emission element 132 impinges only on an inner surface of hollow 135.
Lens case 133 also has gap(s) 136 aground hollow(s) 135 accommodating emission element(s) 132. Light taken in lens case 133 after being emitted sideways from emission element(s) 132 is totally-reflected by slope(s) 137 of gap(s) 136, being directed to a frontal direction. As a result, matrix-type display 130 provide a frontal illumination of an increased brightness.
However, the above-described prior arts involves problems as discussed bellow.                Regarding First Prior Art (Surface Light Source Device 100):        
Emission quantity varies rapidly at parts at which configuration of micro-lens arrays 102 is discontinuously changes and intermediate sections between LEDs 101 side by side are formed. This causes boundary areas between micro-lens arrays 102 to provide conspicuous emission brightness unevenness.                Regarding Second Prior Art (Emission Display 103):        
Continuously arranged plural concave lenses 105 connected to each other are not employed. Further, continuously arranged plural convex lenses 106 connected to each other are not employed. Accordingly, it is difficult to illuminate a large area size object-to-be-illuminated uniformly in a backlighting arrangement.                Regarding Third Prior Art (Display 107):        
Light from LED 108 is affected by converging lens 110 and diverging lens 111 successively. Such successive converging action and diverging action will decrease brightness unevenness as compared with surface light source device 100 (first prior art). However, light from LEDs 108 adjacent to each other is hardly mixed well. Therefore, if LEDs 108 adjacent to each other have emission colors, emission color unevenness between LEDs 108 adjacent to each other tends to be conspicuous.                Regarding Forth Prior Art (Display 121):        
Large wave-like brightness unevenness of illumination light appears as to correspond to cyclic locations of LEDs 124. Such phenomenon is illustrated in FIG. 13. This brings dark parts at intermediate sections between LEDs 124 adjacent to each other, rendering uniform illumination difficult. In addition, directions light fluxes outputted from each LED chip 125 tend to gather neighbourhood of an optical axis of LED 124 corresponding to each LED chip 125.
Such phenomenon is like that observed in a case where an object-to-be-illuminated is directly illuminated by an emission element as shown bay curve S3 in FIG. 13. This results in difficulty such that light fluxes from LEDs 124 adjacent to each other are hardly mixed each other and unevenness in emission color is apt to conspicuous.                Regarding Fifth Prior Art (Matrix-Type Display 130):        
Brightness of frontal illumination light is large. However, light fluxes from lens cases 133 of emission elements 132 adjacent to each other tend to be hardly mixed together. This brings conspicuous unevenness in emission color. In addition, light H emitted from projection portion 134 of lens case 11133 and light H emitted after being totally reflected by slope 137 of gap 136 give a crossover at a location which would be seen easily by naked eyes. As a result, a ring-like locally bright portion can be generated. Such a ring-like locally bright portion would decrease illumination quality.
Saying further, heat generated by emission elements 132 are hardly released because emission device 138 is completely covered by lens cases 133. Therefore, electric components mounted on LCD-panel substrate 131 is apt to be affected by heat.
In addition, some mounting errors can occur in mounting of lens cases 133 to LCD-panel substrate 131 easily, resulting in generation of a gap between lens cases 133 and LCD-panel substrate 131. Such a gap will increase the possibility such that any light enters into lens cases 133 from parts other than the gap. The fifth prior art fails to overcome such undesirable possibility.                Document 1; Tokkai 2002-49326 (JP: See paragraph 0015 and FIG. 4)        Document 2; Tokkai-Sho 59-226381 (JP: See page 3 left-upper column line 15 to right-upper column line 2 and FIG. 6)        Document 3; Tokkai-Sho 63-6702 (JP: See page 2 right-upper column line 20 to left-lower column line 4 and FIG. 3)        Document 4; Tokkai 2001-250986 (JP: See FIG. 1)        